The Analytical Imaging Facility Shared Resource (AIF) provides comprehensive light and electron microscope imaging services to AECCC members. The AIF staff is cross-trained to offer services in classical histology to high-resolution light microscopic imaging in 3D, to state of the art electron microscopy. The electron microscope component offers a full range of specimen preparatory techniques and instrumentation for transmission and scanning electron microscopy. The spectrum of services and technologies include upright light microscopes for imaging in epi-fluorescence, Nomarski (DIC), phase contrast and darkfield. A second component of the facility encompasses scanning confocal- and DIC-based video microscopy with supporting cameras, computers and software to provide digital time-lapse, fluorescence quantitation and other light microscope services involving computer imaging or analysis. This facility was moved to new and enlarged quarters in September, 1998. Over the past funding period a variety of technologies and services have been added. These include quick-freeze fixation followed by high resolution rotary shadowing, quick freeze fixation and freeze substitution, microwave fixation, cryo-ultramicrotomy, and Exhaustive Photon Reassignment deconvolution. Two digital imaging stations have been added to meet the increasing demand for high resolution light microscopy. Most recently, the facility has been funded through an SIG for a multi-photon excitation fluorescence microscope for intravital imaging of live animals and for uncaging in living cells and animals. This system will allow deeper penetration, low photo-bleaching, better signal to noise, speed, and computer networkability. Also, novel high-throughput fluorescence in situ hybridization technologies are now available that allow the quantitative interrogation of sites of transcription within cells with a sensitivity sufficient to detect single molecules, or single nascent transcripts.